Can you try making car2-7 children of each other(car1 is the parent of car2; car2 is the parent of car3; etc) position them accordingly so they are in a single file line and then just itween car 1? Shouldn't that make them all move together? I did not test this so I don't know if this works just going off my itween knowledge/experience.

An almost identical question to this one was asked a few weeks ago, and I don't believed it received any satisfactory answers. You might try using iTween.PointOnPath(). Establish a starting percentage for each of the cars that has them displayed as you want and then manage increment the percentage in code (rather than let iTween manage the movement).